1. Field of the Invention
The present invention relates generally to an ink jet apparatus, and more particularly to a method for determining a printhead gap between a printhead and a sheet of media in an ink jet apparatus that performs bi-directional alignment of the printhead.
2. Description of the Related Art
In prior art, an ink jet printer forms an image on a sheet of media, such as paper, by positioning a printhead in close proximity with the recording medium, and selectively ejecting ink from a plurality of ink jetting nozzles of the printhead to form a pattern of ink dots on the recording medium. During ink jet printing, the printhead is spaced apart from the recording medium in a plane perpendicular to the sheet of media. As the printhead is moved across the sheet of media, from one end to another in a scan direction, ink is selectively ejected from the ink jetting nozzles to form a print swath. After completing at least one print swath, the sheet of media is indexed a selected amount in a sub scan, i.e., paper feed, direction.
Print quality is affected by the bi-directional alignment of a printhead. Bi-directional alignment is performed so that an ink drop may be placed in an exact location, within an accepted tolerance, regardless of whether the ink drop is ejected from the printhead in the forward scan of the printhead or the return scan of the printhead along a bi-directional scan path. Bi-directional alignment is typically performed by printing an alignment pattern with a printhead in both the forward and return scan directions along the bi-directional scan path. The alignment pattern is then read by a sensor, such as a bi-directional alignment sensor, to collect data relating to the placement of ink drops forming the alignment pattern.
Also, a relationship exists between print quality and the spacing, or gap, between the ink jet printhead to the sheet of media, and it is desirable for the printhead to maintain a certain spacing, or gap, relative to the sheet of media. Various factors may influence the size of the gap, including tolerance stack up of manufactured parts, intentional or unintentional variation in recording medium thickness or weight, ambient thermal and humidity conditions, and settling or shifting of printer components due to shipping and setup at the user's premises.